Dried fruit

Berries, apricots, and apples can be easily dried and eaten. They have a higher number of calories per gram and also provide antioxidants and vitamins for a healthier body. As all the water content is removed, and energy-dense fruit is left, making it the best food to gain weight. Dates, figs, and prunes are also some healthy dried fruits. 

The best way to eat them is as snacks. You can make your own dried fruit at home as:
Slice the fruits into strips and remove the seeds.
Cover the fruit in lemon and water.
Bake the fruits between 4 - 12 hours at 145 F.